For several years there has existed a need for a high energy, high power density battery capable of performance at levels of 100 watt-hours per pound and 100 watts per pound. The need for this type of battery has become particularly acute in view of recent fuel shortages. Batteries of this level of performance are required for use in commuter-type automobile vehicles, storage of electrical energy generated during slack consumption periods for use during peak demand, and the like.
It has been known for some time that aqueous systems are not capable of the sustaining high voltages required for such application. Various nonaqueous, solvent systems were attempted, but found to have limited usefulness because of the limited drain rate capability of the call as well as impractical current density levels. These cells have provided energy densities of about 100 watt-hours per pound but only over very long discharge times resulting in poor power capabilities. The power capabilities averaged in the range of from 1 to 20 watts per pound.
Another approach which has been used is the fused salt battery. One such system utilizes a molten LiCl electrolyte in which externally stored chlorine gas is used for reaction with a molten lithium anode. This system has demonstrated very high discharge rates with little polarization losses. However, the system suffers both from a materials corrosion problem as a result of the very high temperatures required, and the need to carry an external source of chlorine gas.
A eutectic fused salt electrolyte of LiCl--KCl has been used with an aluminum-lithium alloy anode and a high surface area carbon cathode. This system has demonstrated relatively good performance, but has been limited by the inherent capacity of the carbon electrode. In particular, the capacity of the carbon cathode is based on its high surface area and its ability to store ions of the electrolyte. Typically, carbon electrodes have a capacity of about 100 to 150 watt-hours per pound. At least one attempt has been made to improve upon the cathode by utilizing elemental sulfur in combination with a porous carbon current collector.
By combining elemental sulfur with the carbon, the battery mechanism is achieved by the formation of lithium sulfide in the presence of elemental sulfur. This battery, however, suffers from a number of shortcomings. For example, the battery cannot be charged to high voltages without chlorine storage becoming significant. Furthermore, it has a high effective resistance, due to the presence of sulfur and lithium sulfide. The cathode itself, sulfur, is soluble in the electrolyte and vaporizes at temperatures above 440.degree.C.
Accordingly, it is an object of the present invention to provide a high energy density fused salt battery that overcomes the disadvantages inherent in the prior art batteries. It is a further object of the present invention to provide a cathode for use in a molten salt battery having high energy storage with no degradation at high voltages, in the chlorine region.